Production of diolefins



March 20, 1945. F. E. FREY PRoDUcTIoN oF DIoLEFINs 2 Sheefs-Sheet 1Filed Aug. 30, 1940 INVENTOR FREDERICK E. FREYV BY i MONEY March 20,1945. F.- FREY 2,371,817

lPRODUCTFON OF DIQLEFINS Filed Aug. so, '1940 2 snets-sheet 2 DOLEFINMMQW Patented Mar'. 2o, 1945 "unimo 4srii'rflis` vParamEor-.1=icla 'e Yl i I ritonuorrzo'limomrms I I' Frederick E. Frey.artlesyille,V)lxla.,l'assinor to Phillips -Petroleum Company, a corporationA ofDelaware Application August 3o, i940, serial No. 354,890

6 Claims. (Cl.l 2GB-881.5)

This'invention relates to the production of diolenn hydrocarbons fromparaflin hydrocarbons by 'dehydrogenation` larly t0 the production ofsuch diolens by the f use of a single dehydrogenation step. Theinventicn has particular reference to the production of diolenns suchasbutadiene'l pentadiene,v andisoprene from the correspondingparainhydrocarbons.4

An appreciable number of diolens such as those just mentioned have beenknown to the art for a number of years. These have been produced in anumber of ways which have included cracking ofheavier oils, thecopolymerization of acetylene and ethylene to form butadiene,'cata lyticor thermal conversion of alcohols, both of the same number of carbonatoms per molecule as the desired diolefln and of a fewer number ofcarbon atoms per molecule, and other more or less involved chemicalprocesses, aswell as the dehydrogenation of the corresponding olefinswhich in turn may have been produced bythe dehydrogenation ofthecorresponding parafllns.

1 This latter procedure, although it appears to be one of the moredirectmethods for the production of diolefins, has not as yet found veryextensive commercial' application, andirlvolves4 a somewhatcomplicatedprocedure including de-` hydrogenation toform oleflns,separation of olefins in a more or less concentrated form,dehydrogenation of these olens to form diolens, and separation of adiolen so produced from unre- It relates more particutial quantities.However, in any clean cut dehydrogenation process the initial products,once formed, vtend to reunite by the reverse reaction of hydrogenation,so that equilibrium value, dependent on the various re'- actionconditions present. For these'reasons, the

maximum value of the'dioleiin concentration, a1- though substantial,will be low.

My invention further comprises various pre- -feried methods ofseparating the dehydrogenation eilluent into the desired constituents.

4 ins disclosure and discussion.

acted olens. However, direct as this process apt pears to be, most ofthe commercial installations to date have been one of the former typesrather than a process involving only direct treatment-ol hydrocarbons ofthe same number of carbon atoms per molecule.

. I havenow found that I can successfully produce substantial yields ofdiolens from -the'corresponding parans by a process which involves asingle dehydrogenation step. In a simple modiiication my invention.comprises passinga parailln hydrocarbon` to a `dehydrogenation stepwhich is adapted to effect a production of di olens, separating most or`all ofthe hydrogen and any light hydrocarbons, from the emuent,

paraiiins together with, the corresponding oleiins which have beenproduced in the dehydrogena- It is an object of my inventionto producediolen hydrocarbons from parailln hydrocarbons hydrogenation whereinoiefins and diolefins, togetherf'with free hydrogen. are produced fromparailin hydrocarbons.

It is another object of this invention to prov duce dilen hydrocarbonsfrom the corresponding parafiin hydrocarbons ofthe lsame number ofcarbon atoms per molecule.

Further objects and advantages'of this invention will become apparentfrom the accompanylnfa preferred form of my invention I employ adehydrogenation catalyst to eifect a production of dioleins. In order toobtain the best yields of dioletlns from my process, and to operate itmostv successfully, I find it necessary to employ onlyT the moreeilicient dehydrogenation catalysts, and toemploy'dehydrogenation-'conditions at which there is only a minimum ofscission of carbon to carbon bonds. 4In this manner I am able toobtainhigh yields or dioienns `or the same number 'of carbon atoms permolecule as the original j paraillns, and also with the correspondingar. rangement of carbon atoms. Furthermore, since Y my inventioninvolvesth production and treat- 'separating and recovering the desireddioleilns so i produced, and returning to the dehydrogenation. ahydrocarbon material comprising uureacted tion. This dehydrogenationstep'apparently does not form the major part of the d'ioleiln product bya dehydrogenaton of a parailln directly to a dlolefin with nointermediate reactions, but ap-4 parently cooperates with the rest of myprocess- 1 vto effect a dehydrogenation of paramns to oleflns andconcomitantly a dehydrogenation of oleilns to diolenns, the latter beingproduced in substan- 55 the most desirable catalysts for my process are.

those that consist of or comprise chromiumoxide,

ment of olen'hydrocarbons corresponding' to the desired diolens, I amable to include in my |process relatively simple separation equipmentfor the recovery of the dioletlns, the` elimination of low.

boiling dehydrogenationv products, and the separation of arecyclefraction composed of paraillns and oleilns. Anydehydrogenationcatalyst with the foregoine` characteristics is suitable for use in myprocess. However, I have found that and especially unglowedchromiumoxide or chromium o xide gel,` which 4is lgenerallydarkI orblack, such as was nrst described byv Huppke. and Frey the concentrationof dehydrogenation products approaches only an in U. S. Patent1.905.383, or a modiiied form of this material as disclosed by Frey andHuppke in U. S. Patent 2,098,959, and is also disclosed in variouscopending applications which include Morey, Serial No. 113,091; Matuszakand Morey, Serial No. 173,708 (Patent No. 2,294,414); Morey and Frey,Serial No. 173,709 (Patent No. 2,312,572); Morey and Frey, Serial No.k359,296, led October 1, 1940, and others. -The dehydrogenation pressureshould not be very high, that is, generally it should not exceed 50 or100 pounds per'square inch gauge, and in most instances should be onlyslightly above atmospheric. At times a subatmospheric pressure varray beused, but although a low pressure favorsthe dehydrogenation reactionsubatmospheric pressures will generally not be used in plant operations.A low partial pressure of the hydrocarbon material present along with atotal pressure above at mospheric may be realized by dehydrogenating thehydrocarbons in admixture with an inert gas such as nitrogen or thelike, as is known to the t art. Although the presence of free hydrogentends tohave an adverse mass action eiect, a small amount of freehydrogen in the charge stock often appears to have a benecial effectupon the catalyst, especially on the initial portions of the catalystwith which the charge stock comes into contact. Other modiiications ofdehydrogenation operation known to the art may also be used. With agiven dehydrogenation pressure and catalyst activity, the-dehydrogenation temperature and reaction time will be interdependentand will have'in general an inverse relationship. 'Ihe dehydrogenationtemperature will be within the range known for catalyticdehydrogenation, but preferably will not be in the upper part of therange but will be between about 700 and 1150 F. Lower temperatures, evenwith long reaction times, willrgive uneconomically low yields, andhigher temperatures, even with very short reaction times, willresult inexcessive formation of low boiling hydrocarbon products. I prefer tooperate under constant conversion conditions with gradually increasingtemperatures as a particular body ofcatalyst becomes deactivated. With asatisfactory dehydrogenation at a relatively low temperature, a iiowrate adapted to give dehydrogenation not far short of equilibrium,'maybe used. If this ow rate is maintained as the temperature is increased,to provide for a relatively constant extent of conversion as thecatalyst becomes less active, the reaction conditions will generally besuch atthe higher temperatures that excessive deleterious secondary orside reactions4 are not encountered.

The paraffin hydrocarbons charged to my process should be in a more orless pure state when it is desired to produce substantially purediolens. My process is particularly adapted to the production ofbutadiene, normal pentadiene, and

isoprene irom'normal butane, normal pentane,

and isopentane respectively. yThese paraiilnhyl- -drocarbons may beconsidered as members of the group 0l Darailns of not more than fivecarbon atoms per molecule and of the type R-CHs-gH-Clr-CHI fresh bodyof'active catalyst, which will produce them, by simplefractionaldistillation and each adapted to eillcient nondestructivedehydrogenation under the conditions disclosed herein. While individualhydrocarbons of a purity greater than 99 per cent may be obtained byfractional distillation, .such purity is often quite expensive to obtainand is generally not necessary for the ordinary commercial applicationof my invention. The recycle feature of my process tends to build upundesirably high concentrations of isomers of the hydrocarbons whichVare being treated by my invention, and the charge stock should besulciently pure that this eiect is not too predominant. This effect isalso readily controlled by periodic or continuous removal andrefractionation of a portion of the recycled hydrocarbon material, aswill be discussed. For most uses of my invention the charge stock willpreferably consist of a hydrocarbon material of a given carbon skeletonstructure in a concentration of at least about per cent of thehydrocarbons present. Although the invention applies primarily to aparaiilnic charge'stock direct from some natural source, if ahydrocarbon fraction is availablewhich contains olens of the same carbonskeleton structure as the paraflins and substantially free lof isomerlcparaiins and/or olens, it will also be a material suitable for chargingto my process, and a hydrocarbon material of a given carbon skeletonstructure will be understood to include such olefins as well as theparaiilns.

My invention will now be more specifically described in connection withthe accompanying drawings, which showv diagrammatically by way of iiowsheets two modifications of apparatus for practicing my invention,

Figure 1 illustrates an arrangement of appaat a relatively low pressureto dehydrogenation unit Il. The dehydrogenation unit Il is comprised ofsuitable heating units or furnaces, catalyst chambers, and the likeknown to the art for effecting and maintaining catalytic nondestructivedehydrogenation o! low boiling hydrocarbons.

The catalyst chambers may be so arranged that heat is supplied to thecatalyst body, or bodies, and the reacting mixture. However, when asteady state of operation is reached only a limited amount ofdehydrogenation actually takes place per pass, since the net amountkwill be the dehydrogenation of a small amount of butane to ,formbutenes and of butenes to form a correspending amount of butadiene, whenthe process is operated to `produce butadiene, and a large substantiallyadiabatic catalyst chamber may be used with an adequate heating of thestream charged to such chamber. 'I'he hydrocarbons charged to theprocess are joined by recycled parailins, and olefins of a like numberof carbon vatoms per molecule` previously produced in thedehydrogenation unit, passing through pipe 32.`

; ing hydrocarbons,v

' dehydrogenation step,

The dehydrogenation is conducted to eiecta dehydrogenation both ofparafllns and oleiins to form olens and diolefins, respectively, alongwith free hydrogen. The resulting products pass through pipe I2 andvalve I3 to the absorber I4, entering at a low point. Absorber I4is-provided with suitable bubblev trays, or packing, or the like, notshowrnknown to the art and suitable for eiectlng intimate contactbetween an ascending ilud and an immiscible descending liquid. Theascending fluid will be either liquid or gaseous, generally gaseous,comprising free hydrogen and paraflln and olefin hydrocarbons of thedehydrogenatlon eluent, and the descending liquid will comprise asuitable absorbent liquid introduced near the top of the absorber,together-with ab sorbed diolefln hydrocarbons. The dehydlogen` l ationeliluent will be suitably cooled before' entering labsorber I4, as bymea-ns of a coolerincorporated as a part of the dehydrogenation unit',or in pipe I2, not shown. The absorption liquid will be likewisesuitably cooled, -by means not shown, such as a` cooler in pipe 51.

A trap-out tray I5 is provided near the bottom of the absorber,preferably below the inlet pipe I2. The rich absorbent liquid, whichwill contain some oleflns as well as the desired diolens, is removed.from the trap-out tray I5 through pipe I6, and Ais passed by suitablemeans through heating coil I1 and pipe I8 to a reboiler 20 whichcomprises the bottom of absorber I4; Vapors, released from the richabsorptlonliquid by this treatment, which will contaiha'higher ratio ofolens to dioleflns than is present in the absorbed material containedinthe liquid passing -through pipe I6, pass up through the trap-out trayI5 to meet the descending 'absorption liquid.

Unabsorbed material, which comprisesV essentially free hydrogen,unreacted paraflins, and oleflns of the same number of carbon atoms permolecule produce by the dehydrogenation, together with possible smallamounts of lower bollpass from a .high point of absorber I4 through pipe23 and valve24, ablycompressed by compressor or pump 25, and passedthrough pipe 26 to separatingI means 21. A-suitable cooling means, 'notshown, may be insertedl in pipe 28 or incorporated asa part of theseparating means 21. The separating means is adapted to eiect aseparation between a hydrocarbon material comprisingessentially paralnsand oleflns'which are to be recycled to the rialcomprising essentiallyfree hydrogen, which is removed from the .process through pipe 30 andvalve 3|. The recycle'stock is withdrawn through pipe 32 and passedthrough valve 33 to pipe I0 to be mixed with a. paraiiin hydrocarbonmaterial If desired, a part or lall charged to the process.' of thestream may be used to effect a part of the ycooling required inconnection' with separating means I21, this being accomplished bypassing the liquid stream through pipe 34. and valve 35 to and a lowerboiling mateliquid in reboiler is suitf vaporizing or cooling coll 88,and then through y pipe 81 Vaud valve valve 83 being partly orcompletely closed, A1.. though it i's primarilyfintended to treata'single paraffin hydrocarbon, it is generally not economical to isolatesuch a material' in acompletely pure state, though it is nottoodiilicultor expensive to Produce terial which is 95'to 9'7 percentpure. I have found such a' charge to be of a satisfactory purity.However, impurities present in this charge. tend to build up inthesystem, so that it is often de- 38 back `to pipe 32, with the sirable toremove a continuously or intermittently from pipe moved may be subjectedto further separation, with the desired, recovered hydrocarbons beingreintroducedto the system with fresh paraiiins through pipe Il).

The rich absorption diolens, is removed from the reboiler 20 throughpipe 42 and .passes through valve 43 to -the top of a first stripperv44. A portion only of the absorbed material is removed in this stripper,and will com prise a substantial portion of ldioleiin together with themajor part 'of any remaining absorbed olen. The material so removed isreturned, at least in part, through pipe 45 and valve 4B to the ratedmaterial may be removed from the system through pipe 41 and valve 4 8,if desired,for further treatment. The partially stripped rich absorbentpasses from a low point of stripper 44 through pipe 50 and valve 5I 'tostripper 52, wherein itis completely freedofabsorbed hydrocarbons. Thematerial so removed will comprise essentially the desired dioleiin'andis recovered as a product of the process through pipe 53 andivalve 54.As an'aid to the concentration of diolein in the original richabsorbent, and removal of undesired absorbed oleiins, a portion of thisdiolen material may be returned to the reboiler 2li `from pipe 53through pipe 55 and valve 56. The denuded lean absorbent liquid isremoved from 'a' low point of stripper 52 through pipe 51 andvalve 58 toa high point of absorber I4. Any heaviery hydrocarbons which may beformed in the dehydrogenatlon step in small amounts will 'collect inthis absorption oil and build up in the system. Any such accumulationmay be controlled andlmited by withdrawing' av portion ofthe leanabsorption oil from the system through pipe 5I and valve 82, andremoving such heavy hydrocarbons, and if desired returningthe purifiedoil-to the,V system by means not shown.

The procedure just described for the apparatus shown in Figure 1 is forthe process'which has reached a steady state of operation. In initiallystarting the dehydrogenation step,- only a small amount of diolen willbeformed, and it will gen` erally be desirable to recycle the entirehydroca bon material for a short period. This can be done by use of theby-pass -2I with valve 22' open and with valve I3 partially orcompletely closed.

.At this time aswell as during subsequent steadystate operation, it maybe desirable to include a small amount 4of free hydrogen in therecyclestream passing through pipe 32, so that the initial part ofthe catalystbed or beds used in the de:

hydrogenatlon unit II will operate in the presence of small amounts offree hydrogen. aswell as subsequent portions ofsaid'beds. Afterthefdiolefin concentration of the eilluent has risen to an lappreciablevalue, such as 3 or 4 to 6 or 8 per cent, the eilluent is passedto theabsorber, as discussed.

The absorption liquid used in absorber I4 is one 4in which unsaturatedhydrocarbons are preferentially dissolved and parailn hydrocarbons areonly slightly soluble. It is desirable that this absorption medium haveonly a limited capacity for by fractional distillation a masolution evenof theunsaturated hydrocarbons,

otherwise the resulting solution-will tend to' be completely" misciblewith all hydrocarbons 4after taking up an appreciable quantity' ofunsaturated hydrocarbons. uhiscan be somewhat limited and controlledbyoperating at a suitably low tem- 4 3 portion of the recycle stock, i.

liquid, containing desired 20. A portion of this unsatu-l trays orpacking or to ascending gases and vapors. Free hydrogen,

will tend to increase at ilrst upon the absorption of diolefins butwhich I have found can be counteract/ed and suitably controlled byproper control of temperature and pressure of the rich absorbent,together with judicious recycling of various streams as has just beendescribed in connection with Figure l. 'Ihe rich absorbent, containingsome mono-olens as well as the desired dioleflns, which collects on trayI5, is heated and returned to reboiler wherein it has added to it diolenconcentrates introduced through pipe 'and/or pipe 55. 'Ihis treatmenthas the effect of vaporizing absorbed mono-olelns both as a result ofthe heating and of the increased concentration of diolen. Mono-oleflnswhich remain and are present in the material passed through pipe 42 aresubstantially completely removed in the preliminary stripper` 44.

Although some dioleiin is likewise vaporized at this point, it isrecovered within the system, as will be readily appreciated, and afterthe absorption and recovery system has reached a steady state ofoperation the stream passing through pipe 23 will be substantially freeof diolefn and contain mono-oleiin equivalent in amount to that .g

present in the stream entering the bottom of the absorber through valveI3. Likewise, the stream recovered as a product of the process throughpipe 53 and valve 54 will comprise diolelns in high concentration and inan amount equivalent to that produced by the dehydrogenatin and enteringthe absorber through valve I3', an amount which will also be practicallyequivalent to the fresh hydrocarbon material of the samecarbon skeletonstructure charged to the process through along with any light gases, isremoved through pipe 30 and valve 3|. A rich absorption liquid passesfrom a low point of the absorber II4 through pipe I I5 and valve IIB toa high point of stripper II1. The absorbed hydrocarbons are removed fromthe absorption liquid, and thisr latter passes in a. lean state from alow point of stripper ||1 through pipe ||8 and valve ||9 to the top oflabsorber I I4.

Any heavier hydrocarbons which may be formed in the dehydrogenation stepin small amounts will collect in this absorption oil and build up in thesystem. Any such accumulation may be conf trolled and limited bywithdrawing a portion of the lean absorption oil from the system throughpipe |2-6 and valve |21, and removing suchheavier hydrocarbons, and ifdesired returning the purifled oil to the system by means not shown.

The hydrocarbon material so removed, which comprises essentiallyparaiiins, olens, and diolefns of the same number of carbon atoms permolecule, passes through pipe |30 and valve I3I to a second separatingmeans such as the absorber or fractionator I32. When vused as anabsorber,

it is preferably used in conjunction with a material which reactsselectively with diolens to form a readily decomposable chemicalcompound. Such materials are known to the art and include aqueoussolutions or compositions Iof a salt of a heavy metal of groups I and IIof the periodic system, especially of suchl a metal in monovalent form;as a. cuprous halide, or a mercurous or silver salt, and especially anaqueous alkaliehalid'e-containing solution, or suspension, of cuprouschloride. Such a material is introduced near the top of absorber |32 andis intimately mixed, as it passes downwardly, with ascending hydrocarbonmaterial. A hydrocarbon material comprising espipe I0. If the absorbentis suiciently selective in its action, the primary stripper y44 may beomitted, and the rich absorbent passed directly from pipe 42 throughpipe 53 and valve 60 to pipe and stripper 52.

Referring now to Figure 2, this shows an alternative but not completelyequivalent recovery process for recovering the desired diolefln product,the dehydrcgenation step being substantially the same as that .lustdescribed in connection with Figure 1. A suitable hydrocarbon materialenters the system through pipe I0 and is passed atl a relatively lowpressure to dehydrogenation unit I I, as previously discussed. Theparaflins charged to the process are joined by recycled paraiins, andoleflns of a like number of carbon atoms per molecule previouslyproduced in the dehydrogenation unit, passing through pipe 32. Thedehydrogenatlon products pass through pipe I2, compressor |25, and valve||3 to separating means illustrated by absorber II.4, entering at a lowpoint. Absorber ||4 is equipped with suitable bubble the like, and isoperated primarily to effect a separation between free hydrogen and anylight gases on the one hand, and dI- oleiins, olens, and unreactedparalns on the other. If a single absorber is used. as shown, this maybe accomplished by passing a relatively nonselective absorption liquidtothe top of the absorber, letting it pass downwardly countercurrentsentially parains and olens passesr from the top of absorber I32 throughpipe 32, and is passed through valve 33 to pipe IU, to be mixed with thehydrocarbon material charged to the process. If desired a part or all ofthis material may be used to eiect a part of the cooling required inconnection with separating means II4, especially if the material passingthrough pipe 32 is in the liquid state and is substantially above thepressure required in the dehydrogenation unit I This cool-r ing may' becarried'out by passing the material through pipe 34 and valve 35 tocooling coil 38, and then through pipe 31 and valve 38 back to pipe 32with the valve 33 beingpartly or completely closed.' As previouslymentioned in connection with Figure 1,l a portion of this stream may becontinuously or intermittently removed through pipe 40 and valve 4I forfurther separation of its components.

A solution or slurry containing the resultant diolefin complex passesfrom absorber |32 through pipe I 33 and valve I 34 to stripperl |35,wherein the diolen is separated from the complex compound, as byheating, and is recovered as a product of the process through pipe |36andvalve |31. The other component of the complex compound is recoveredand returned to the absorber I3`. through pipe |38 and valve |39.

This procedure is adapted to the production and separation of all lowboiling diolefins which are readily produced by the catalyticdehydrogenaltion of paraillns and olens. In the case of the means |32may be operated as a fractonator, in

this case, andthe higher boiling pentadiene may be recovered by simplefractional `distillation from the lower boiling normal pentaneandpentenes.' In such a case, the normal pentane and pentenes passoverheadthrough pipe 32, and pentadiene is `desirable at the start of arun to recycle a por-4 tion or all of the dehydrogenation ellluent, orof the hydrogen-freed hydrocarbon material, for a short period. Recycleof `Vthe entire vriiiuent can be effected by use of the bypass |2| withvalve |22 open and valve l| |3 partially cr completely closed. Recycleof unseparated hydrocarbon material may be readily realized by 'removalof a part or all of the stream normally entering separating means |32,by means not shown, and returning it to thc processthrough pipe '|0. Y

`As an example of the operation of one mcdcation of my process, a butanestream compris- :ng about 97 per cent normal butane, with the remainderprimarily isobutane, may be passed at a temperature of about 950 F. overa large mass of dehydrogenation catalyst comp'ising a dried and reducedmixed gel cf chromium oxide and aluinizia, prepared as described in U..S. Patent 2,098,959 to Frey andHuppke. cn an inert granular support. Thepressure .is only sufficiently above by volume, about 15 per cent eachof hydrogen and normal bute'nes. the remainder being primarily unreactedbutane with a practically negligible quantity of butadiene. Freehydrogen is removed from this initial eiiluent by simple cooling andliquefaction of the C4 hydrocarbons, with the C4 hydrocarbon material sorecovered being returned directly to the inlet of the dehydrogenationstep. As the products of th's first recycle portion of the continuouscharge stream appear in the eiiluent the butadiene content of theeiiiuent, produced by dehydrogenation of butenes. rapidly approaches avalue of about 4.5 per cent.'y with about 65 pei-'centr unreactedbutaneV and about 18 per cent butenes, the remainder beiner essentiallyfree hydrogen. Atthis stage of the operatiomin addition to the removalofv free hysuiiicient to .maintain a substantiallyconstant amountof'conversion, and as the maximum temperature is reached afresh catalystmass, at an initial temperature again of about 950o F. is

switched into operation. As the process reaches a steady state ofoperation the total charge, including added butane, and the efiiuenthave approximately the following compositions, in per cent by volume ofthe gaseous mixture.,`

Component Elliuent Charge C4H|o 60 75- CHg 22 i 25 'C4H(Butadiene) 6About 2 per cent ofthe recycle C4 hydrocarbon mixture is'continuously`discarded from the process, thereby maintain-'ng the normal C4hydrocarbons in the total charge at a value greater than 95 per cent.

l As previously mentioned, the carried out in unit is conducted under arelatively'low pressure, which should not appreciably exceed about 50erl00pounds per square inch gauge, and which in most instances will benearer atmospheric ypressure andmay even be subatmospheric. In manyinstances, therefore, the dehydrogenation pressure will be less than thepressureof the source of the material charged through pipe i0, and apump or compressor will not be necessary for this stream. A compressor25 has been shown in Figure 1, and a compressor |25I in Figure 2. Formost adaptations of my invention such compression of part or all of thedehydrogenation 'efiluent will be the only compression and pumping usedon the stream which contain or compriseolens and unreacted parafilnsdestined to be recycled to the dehydrogenation i unit a feature which isone of the advantages drogen from the eiiluent, the' eiiluent is alsolittle over 20 ,per cent butenes, is recycled to the inlet of thedehydrogenation step, with additional normal butane being added in anamount sub'- stantially equivalent to the butadiene removed. so thatthetotal quantity of C4 hydrocarbon` maconstant.- As the dehydrogenationcatalyst mass loses activity,the temperature of the charge is raised toa maximum of about 1050 F. at a rate of my process. pressors for otherstreams have not been shown, the general` flow of the various streams isindicated and has been discussed, and suitable mechanical equipment oiAthis nature can be readily supplied as required in any particularapplication of my invention by'one skilled inthe art. Similarly, otherunits of .eduipment have been shown only diagrammatically, but havebeendescribed and the functions explained sofas to serve as suitableguides for adaptation of suitable specie )equipment for specificinstallations. It will be obvious t0 those skilled in the art thatvarious modifications of my invention may be practiced as being includedin the spirit of the disclosure and in the ,scope of the claims.y

I claim:

1. An improved processfor the separation-of butadiene produced by the.dehydrogenationmof normal C4 hydrocarbons from accompanying de-VUhydrogenation products, which comprises 'passing 1 theeiiiuent from sucha dehydrogenation to a low-point of an'absorber, passing toa highpointof said absorber a lean selective-absorption liquid to effect-aselective absorption of unsaturated!"` hydrocarbons, removingunabsorbed. gases from f the absorber, passing -a rich. absorbent.liquidM stream from saidabsorbent step to a rst stripper, effecting insaid first stripper a partial stripterial subjected to dehydrogenationis `maintained i ping of said rich absorbent to remove therefrom a lessunsaturated hydrocarbon material and re turning at leasta portion of thesame to -a low' u `point or said absorber, passing the ,resultantpardehydrogenation Although other pumps or com-v a high point of saidabsorber a lean selective absorption liquid to euect a selectiveabsorption of l unsaturated hydrocarbons, removing unabsorbed che'low-boiling diolen of four to uve carbon atoms" per molecule, producedby the dehydrogenation of a corresponding more saturated-hydrocarbon,from accompanying dehydrogenation products, which comprises passing theeilluentfrom such a dehydrogenation to a low point of an absorber.passing to a high point of said absorber a lean selective absorptionliquid to effect a selectiye' absorption of unsaturated hydrocarbons,remov-V- ing unabsorbed gases from the system, passing a rich absorbentliquid stream from said absorbent step to a rst stripper, effecting in-said irst stripper a partial stripping of said rich absorbent to removetherefrom a less unsaturated hydrocarbon material and returning at leasta portion oi' the same' to a low point of said absorber, passing theresultant partially stripped rich absorbent liquid to a second stripper.removing therefrom remaining absorbed material comprising predominantlydoleiins, passing. a resultant lean absorption liquid to a high pointoilsaid absorber, returning a portion of said separated absorbed diolenmaterial to a low point of said absorber, andremoving from the processas a dioleiln product a further portion of said material.

3. An improved process for the separation of a low-boiling diolen offour to ve carbon atoms per molecule, produced by the dehydrogenation ofa vcorresponding more saturated hydrocarbon, from accompanyingdehydrogenation products, which comprises passing the ,eiiiuent -fromsuch a dehydrogenation to a low point of an absorber, passing to a highpoint of said absorber a lean selective absorption liquid to eiect aselective absorption of unsaturated, hydrocarbons, removing unabsorbedgases from the system, heating the rich absorption liquid at the bottomof said absorber to vaporize a portion of the material absorbed therein,passing from the bottom of said absorber a rich absorption liquid streamto a first stripper, eiecting in said rst stripper-a partial strippingof said rich absorption liquid t'o remove therefrom lessv unsaturatedhydrocarbon material and returning at least a portion of the same'to theheated liquid in the bottom of said absorber, passing the resultantpartially stripped rich absorption liquid to a second stripper, removingtherefrom remaining absorbed material comprising predominantly diolens,passing a resultant lean absorption liquid to a high point of saidabsorber, returning a portion of said separated diolefin material to theheated liquid in the bottom of said absorber, and removing from theprocess a further portion or said materialas a diolein product.

4. An improved process for the separation of pentadiene produced by thedehydrogenation of the corresponding Cs hydrocarbons from accompanyingdehydrogenation products, which com l prises passing the eiiiuent fromsuch a dehydrogenation to a low point of an absorber, passing to gasesfrom the absorber, passing a rich absorbent liquid stream from saidabsorbent step to a ilrst stripper, effecting in said first stripper apartial stripping of said rich absorbent to remove there- `from a lessunsaturated hydrocarbon material and returning at least a portion of thesame to a low point of said absorber, passing the resultantpartilally-stripped rich absorbent liquid to a sec-` ond stripper,removing therefrom remaining absorbed materials comprising predominantlypentadiene, passing a resultant lean absorption liquid to a high pointo! said absorber, returning a portion of said separated absorbedpentadiene material to a low point oi said absorber, and removing fromthe process as a pentadiene product a further portion of said material.

5, An improved process for the separation of normal pentadienel producedby vthe dehydro sorbed gases from the absorber, passing a rich absorbentliquid stream from said absorbent step to a rst stripper, effecting insaid iirst stripper av partial stripping of said rich absorbent toremove therefrom a less unsaturated hydrocarbon material and returningat least a portion of the same to a low point of said absorber, passingthe resultant partially stripped rich absorbent liquid to a secondstripper, removing therefrom remaining absorbed material comprisingpredominantly normal pentadiene, passing a resultant lean absorptionliquid to a high point of said absorber, returning a portion of saidseparated absorbed normal pentadiene material to a low point of saidabsorber, and removing from the process as a normal pentadiene product afurther portion of said material.`

6. An improved process for the separation of isoprene produced by thedehydrogenation of the corresponding more saturated Cs hydrocarbons fromaccompanying dehydrogenation products, which comprises passing theefiluent from such a dehydrogenation to a low point of an absorber,passing to a high point of said absorber a lean selective absorptionliquid to eiiect a selective absorption of unsaturated hydrocarbons,removing unabsorbed gases from the absorber, passing a rich absorbentliquid stream from said absorbent step to a first stripper, effecting insaid first stripper` a partial stripping of said rich absorbent toremove therefrom a less unsaturated hydrocarbon material and returningat least a portion of the same-to alow point of said absorber, passingthe resultant partially stripped rich. absorbent liquid to a secondstripper, removing therefrom remaining absorbed material comprisingpredominantly isoprene, passing a resultant lean absorption liquid to ahigh point of said absorber, returning a portion of said separatedabsorbed isoprene material to a low point of said absorber, and removingfrom the process as an isoprene product a further portion of saidmaterial.

FREDERICK E. FREY.

